A focal point detection device in a single lens reflex camera in the related art typically adopts the split pupil image reforming method (see patent reference literature 1 and the like). In this method, images are individually reformed via a pair of image reforming lenses by using image forming light fluxes having been transmitted through different areas on the exit pupil of the photographic lens of the camera, the patterns of the pair of secondary images thus reformed are detected with a line sensor and a defocus signal is generated based upon the extent of pattern misalignment manifested by the pair of the secondary images.
In this method, the detection pitch at the focal point detection plane (predetermined focal plane), i.e., the pixel pitch of virtual pixels achieved by reverse-projecting (projecting the line sensor back onto the focal point detection plane via the image reforming lenses), is determined in correspondence to the projection magnification rate and the pixel pitch with which the pixels at the line sensor are disposed. Accordingly, by disposing pixels in a very dense array at the line sensor, very accurate focal point detection is enabled.
It is to be noted that the term “focal point detection plane” refers to a plane at which focus adjustment is attempted, e.g., a plane conjugate with the film surface.
Patent reference literature 1: Japanese Laid Open Patent Publication No. 2002-174766